This invention relates generally to a dispensing apparatus for fluid products and more particularly, to a hand held gun which mixes and dispenses two fluid components.
The invention is particularly applicable and will be described with specific reference to a hand held dispensing gun for dispensing a two-component polyurethane foam. However, the invention in its broader application is not limited to polyurethane foams but has application to mixing and dispensing multi-component chemicals such as polyvinyls, paints, etc.
This invention is particularly suited for in situ applications of liquid chemicals mixed and dispensed as a spray or a foam and more specifically, to in situ application of polyurethane foam or froth. In situ applications for polyurethane foam have continued to increase in recent years extending the application of polyurethane foam beyond its traditional uses in the packaging, insulation and molding fields. For example, polyurethane foam is being used with increasing frequency as a sealant in the building trades for sealing spaces between windows and door frames and the like and as an adhesive for gluing flooring, roof tiles, and the like.
Polyurethane foam for in situ applications is typically supplied as a xe2x80x9cone-componentxe2x80x9dfroth foam or a xe2x80x9ctwo-componentxe2x80x9d froth foam in portable containers hand carried and dispensed by the operator through either a valve or a gun. However, the chemical reactions producing the polyurethane froth foam in a xe2x80x9cone-componentxe2x80x9d polyurethane foam is significantly different than the chemical reactions producing a polyurethane froth foam in a xe2x80x9ctwo-componentxe2x80x9d polyurethane foam. Because the reactions are different, the dispensing of the chemicals for a two-component polyurethane foam involves different and additional concepts and concerns than that present in the dispensing apparatus for a xe2x80x9cone-componentxe2x80x9dpolyurethane froth foam.
A xe2x80x9cone-componentxe2x80x9d foam generally means that both the resin and the isocyanate used in the foam formulation are supplied in a single pressurized container and dispensed from the container through a valve or a gun attached to the container. When the chemicals leave the valve, a reaction with moisture in the air produces a polyurethane froth or foam. Thus, the design concerns related to an apparatus for dispensing one-component polyurethane foam essentially concerns the operating characteristics of how the one-component polyurethane foam is throttled or metered from the pressurized container. Reference, for example, can be had to U.S. Pat. No. 5,887,756 to Brown, issued Mar. 30, 1999 and U.S. Pat. No. 5,645,199 to Schnitzler, issued Jul. 8, 1997. While one-component guns can variably meter the polyurethane froth, they are typically used in caulk/glue applications where an adhesive or caulk bead is determined by the nozzle configuration. Post drip is a major concern in such applications as well as the dispensing gun not clogging because of reaction of the one component formulation with air (moisture) within the gun. To address or at least partially address such problems, a needle valve seat is typically applied as close to the dispensing point by a metering rod arrangement which can be pulled back for cleaning. While metering can occur at the needle valve seat, the seat is primarily for shut-off to prevent post drip, and depending on gun dimensioning, metering may principally occur at the gun opening.
In contrast, a xe2x80x9ctwo-componentxe2x80x9d froth foam means that one principal foam component is supplied in one pressurized container, typically the xe2x80x9cAxe2x80x9d container (i.e., polymeric isocyanate, fluorocarbons, etc.) while the other principal foam component is supplied in a second pressurized container, typically the xe2x80x9cBxe2x80x9d container (i.e., polyols, catalysts, flame retardants, fluorocarbons, etc.) Examples of two-component dispensing guns in commercial use today may be found in assignee""s U.S. Pat. No. 5,429,308, to Brown, issued Jul. 4, 1995 and U.S. Pat. No. 5,242,115 to Brown, issued Sep.7, 1993. Additional commercial applications include U.S. Pat. No. 5,462,204 to Finn, issued Oct. 31, 1995; U.S. Pat. No.5,129,581 to Braun et al., issued Jul. 14, 1992; and, U.S. Pat. No. 4,925,107 to Brown, issued May 15, 1990. These guns are improvements over early two-component dispensing gun designs such as shown in U.S. Pat. No. 2,890,836 to Gusmer et al., issued Jun. 16, 1959; United States Pat. No. 3,559,890 to Brooks, issued Feb. 2, 1971; and, U.S. Pat. No. 3,784,110 to Brooks, issued Jan. 8, 1974.
In a two-component polyurethane foam, the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d components form the foam or froth when they are mixed in the gun. Of course, chemical reactions with moisture in the air will also occur with a two-component polyurethane foam after dispensing, but the principal reaction forming the polyurethane foam occurs when the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d components are mixed or contact one another in the dispensing gun. The dispensing apparatus for a two-component polyurethane foam application has to thus address not only the metering design concerns present in a one-component dispensing apparatus, but also the mixing requirements of a two-component polyurethane foam.
Further, a xe2x80x9cfrothingxe2x80x9d characteristic of the foam (foam assumes consistency resembling shaving cream) is enhanced by the fluorocarbon (or similar) component, which is present in the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d components. This fluorocarbon component is a compressed gas which exits in its liquid state under pressure and changes to it gaseous state when the liquid is dispensed into a lower pressure ambient environment, such as when the liquid components exit the gun and enter the nozzle.
While polyurethane foam is well known, the formulation varies considerably depending on application. In particular, while the polyols and isocyanates are typically kept separate in the xe2x80x9cBxe2x80x9d and xe2x80x9cAxe2x80x9d containers, other chemicals in the formulation may be placed in either container with the result that the weight or viscosity of the liquids in each container varies as well as the ratios at which the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d components are to be mixed. In the dispensing gun applications which relate to this invention, the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d formulations are such that the mixing ratios are generally kept equal so that the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d containers are the same size. However, the weight, more importantly the viscosity, of the liquids in the containers invariably vary from one another. To adjust for viscosity variation between xe2x80x9cAxe2x80x9dand xe2x80x9cBxe2x80x9d chemical formulations, the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d containers are charged (typically with an inert gas) at different pressures to achieve equal flow rates. The metering valves in a two-component gun, therefore, have to meter different liquids at different pressures at a precise ratio under varying flow rates. For this reason (among others), some dispensing guns have a design where each metering rod/valve is separately adjustable against a separate spring to compensate not only for ratio variations in different formulations but also viscosity variations between the components. The typical two-component dispensing gun in use today can be viewed as two separate one-component dispensing guns in a common housing discharging their components into a mixing chamber or nozzle. In practice, assignee has determined that invariably the gun operator adjusts the ratio settings to improve gun xe2x80x9cperformancexe2x80x9d with the expected poor result. To counteract this adverse result, the ratio adjustment then has to be xe2x80x9chiddenxe2x80x9d within the gun, or the design has to be such that the ratio setting is xe2x80x9cfixedxe2x80x9d in the gun for specific formulations. The gun cost is increased in either event and xe2x80x9cfixingxe2x80x9d the ratio setting to a specific formulation prevents interchangeability of the dispensing gun.
Besides the ratio control which distinguishes two-component dispensing guns from one-component dispensing guns, a concern which affects all two-component gun designs (not present in one-component dispensing guns) is known in the trade as xe2x80x9ccross-overxe2x80x9d. Generally, xe2x80x9ccross-overxe2x80x9d means that one of the components of the foam (xe2x80x9cAxe2x80x9d or xe2x80x9cBxe2x80x9d) has crossed over into the dispensing mechanism in the dispensing gun for the other component (xe2x80x9cBxe2x80x9d or xe2x80x9cAxe2x80x9d). Cross-over may occur when the pressure variation between the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d cylinders becomes significant. Variation can become significant when the foam formulation initially calls for the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d containers to be at high differential charge pressures and the containers have discharged a majority of their components. (The containers are accumulators which inherently vary the pressure as the contents of the container are used.) To overcome this problem, it is known to equip the guns with conventional one-way valves, such as a poppet valve. While necessary, the dispensing gun""s cost is increased.
Somewhat related to cross-over and affecting the operation of a two-component gun is the design of the nozzle. The nozzle is a throw away item detachably mounted to the gun nose. Nozzle design is important for cross-over and metering considerations in that the nozzle directs the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d components to a static mixer in the gun. One gun described in U.S. Pat. No. 5,462,204 completely divides the nozzle into two passages by a wall extending from the nozzle nose to the mixer. The wall lessens but does not eliminate the risk of cross-over since the higher pressurized component must travel into the mixer and back to the lower pressure metering valve before cross-over can occur. However, the nozzle design illustrated in U.S. Pat. No. 5,462,204 patent may be limited because of the wall and nozzle inlet chamber tending to create turbulence for applications requiring very high flow rates.
A still further characteristic distinguishing two-component from one-component gun designs resides in the clogging tendencies of two-component guns. Because the foam foaming reaction commences when the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d components contact one another, it is clear that, once the gun is used, the static mixer will clog with polyurethane foam or froth formed within the mixer. This is why the nozzles, which contain the static mixer, are designed as throw away items. In practice, the foam does not instantaneously form within the nozzle upon cessation of metering to the point where the nozzles have to be discarded. Some time must elapse. This is a function of the formulation itself, the design of the static mixer and, all things being equal, the design of the nozzle.
The dispensing gun of the present invention is particularly suited for use in two-component polyurethane foam xe2x80x9ckitsxe2x80x9d typically sold to the building or construction trade. Typically, the kit contains two pressurized xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d cylinders of about 7xc2xd inches in diameter which are pressurized anywhere between 150-250 psi, a pair of hoses for connection to the cylinders and a dispensing gun, all of which are packaged in a container constructed to house and carry the components to the site where the foam is to be applied. When the chemicals in the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d containers are used up, the kit is sometimes discarded or the containers can be recycled. The dispensing gun may or may not be replaced. Since the dispensing gun is included in the kit, kit cost considerations dictate that the dispensing gun be relatively inexpensive. Typically, the dispensing gun is made from plastic with minimal usage of machined parts.
The dispensing guns cited and to which this invention relates are additionally characterized and distinguished from other types of multi-component dispensing guns in that they are xe2x80x9cairlessxe2x80x9d and do not contain provisions for cleaning the gun. That is, a number of dispensing or metering guns or apparatus, particularly those used in high volume foam applications, are equipped or provided with a means or mechanism to introduce air or a solvent for cleaning or clearing the passages in the gun. The use of the term xe2x80x9cairlessxe2x80x9d as used in this patent and the claims hereof means that the dispensing apparatus is not provided with an external, cleaning or purging mechanism.
While the two-component dispensing guns discussed above function in a commercially acceptable manner, it is becoming increasingly clear as the number of in situ applications for polyurethane foam increase, that the range or the ability of the dispensing gun to function for all such applications has to be improved. As a general example, the dispensing gun design has to be able to throttle or meter a fine bead of polyurethane froth in a sealant application where the kit is sold to seal spaces around window frames, door frames, and the like in the building trade. In contrast, where the kit is sold to form insulation, an ability to meter or flow a high volume flow of chemicals is required. Still yet, in an adhesive application, liquid spray patterns of various widths and thickness are required. While the xe2x80x9cAxe2x80x9dand xe2x80x9cBxe2x80x9d components for each of these applications are specially formulated and differ from one another, one dispensing gun for all such applications involving different formulations of the chemicals is needed.
Accordingly, a principal object of the present invention is to provide an improved, airless two-component dispensing gun, suitable for use with any number of two-component polyurethane foam formulations requiring metering of the foam over a wide flow range.
This object along with other features of the present invention is achieved in an airless, two-component polyurethane foam dispensing gun which includes a body having a longitudinally-extending valve portion containing a pair of laterally displaced, generally parallel, and straight, longitudinally-extending tubular dispensing passages, each dispensing passage having a conical valve seat at one end and an open end at its opposite end which, in turn, forms a metering rod opening in the body. A generally straight feed passage extends along a feed passage axis for each dispensing passage and each feed passage has a discharge end in fluid communication with a dispensing passage between the dispensing passage""s valve seat end and the metering rod opening. The feed passage axis forms an acute angle of less than about 30xc2x0 with the dispensing passage. A longitudinally-extending metering rod is positioned in each dispensing passage with the metering rod having a conical valve tip at one end, a yoke collar section at its opposite end and an intermediate tubular seating section for sealing and guiding the metering rod within the dispensing passage. A nozzle is detachably connected in a sealing manner to the nose portion of the gun and has an outlet tip at one end, an inlet chamber at its opposite end and a static mixing chamber containing a static mixer therebetween. A spring is in contact with the yoke collar of each metering rod and biases the valve tip of each metering rod into contact with the valve seat of each dispensing passage and a manually operable trigger moves the metering rod against the bias of the spring. The arrangement of the feed and dispensing passages minimizes turbulent flow of the components as they travel through and are metered from the gun permitting the gun to better achieve ratio control over a wide flow range, as well as the maximum flow output allowable by the viscosity/gas pressure combination of the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d components.
In accordance with another aspect of the invention, the gun body has a transversely extending handle portion, a longitudinally-extending, open ended spring portion generally aligned with the dispensing passages and generally transversely adjacent the handle portion and a longitudinally-extending trigger recess portion between the body""s valve portion and the spring portion. A trigger having a trigger yoke crossbar portion is received within the trigger recess and a trigger lever portion transversely extends from the crossbar. The crossbar has a pair of laterally spaced metering rod openings through which the intermediate sections of each metering rod extends. The trigger also has a trigger pivot portion transversely extending from the crossbar in a direction opposite the trigger level and the trigger pivot extends into a generally U-shaped portion of the recess which is transversely spaced from the metering rods to provide a xe2x80x9cfloatingxe2x80x9d pivot. The metering rods have a yoke collar section at their end opposite the end containing their conical valve tip and are larger in diameter than the metering rod openings in the crossbar. The yoke collar section has an annular collar surface extending radially outward at the intersection of the metering rods intermediate section which is sealingly and slidably disposed within and extends from the dispensing passage. The annular collar surface is adjacent the yoke crossbar and is chamfered at a set angle to produce a cam pivot which provides increased rotational movement of the trigger lever about the trigger pivot which allows for better operator control in fine metering applications while the crossbar positively assures equal movement of both metering rods.
In accordance with another feature of the invention, improved variable metering of flow occurs throughout the entire length of trigger actuation and beyond the fine metering characteristics of the dispensing gun. The metering rods conical valve tip end section includes a generally cylindrical tip portion ending in a truncated conical portion, in turn, ending in a larger cylindrical portion which, in turn, ends in the intermediate sealing section of the metering rod which extends through the yoke crossbar""s opening. The valve seat in the dispensing passage is formed as a frusto-conical valve seat so that retraction of the metering rod in the dispensing passage opens the conical valve seat in the normal manner. The design advantageously utilizes the physical properties of two component polyurethane foams. Specifically, the xe2x80x9ccompressed gasxe2x80x9d components of the liquid xe2x80x9cAxe2x80x9d and/or xe2x80x9cBxe2x80x9d components (i.e., fluorocarbons) changes from a liquid state to a gas state and the pressurized liquid exits the pressurized environment of the gun into the ambient (lower pressure) environment of the nozzle. As the metering rods (needles) are pulled back, an ever increasing volume of pressurized liquid is moved closer to the cylindrical valve seat opening and the lower pressure environment of the nozzle. In so doing, the compressed gas component in the liquid phase beings to expand to the gaseous state, providing an increasing amount of back pressure exerted on the liquid chemicals. The invention recognizes and utilizes this characteristic of two component polyurethane foams, by maintaining the truncated conical portion of each metering rods within the frusto-conical valve seat throughout the longitudinal travel of the metering rod to obtain desired metering. Importantly, the conical angles (of the valve seat and truncated conical portion of the metering rod) are maintained at acute angles not greater than 10xc2x0 and the dimensioning of the components is such that the orifice of the dispensing gun continuously increases as the gun is progressively actuated with full throttle establishing an orifice size equal to or less than the area of the frusto-conical valve seat at its minor diameter. That is, metering occurs between frusto-conical valve seat and cylindrical tip portion of metering rod through dispensing gun travel and not at the minor diameter opening of the frusto-conical valve seat.
In accordance with an alternative embodiment feature of the invention, the frusto-conical valve seat may have a cylindrical opening extending from its minor diameter which receives the cylindrical tip portion of the metering rod when the conical portion of metering rod seats against the frusto-conical valve seat in an xe2x80x9coffxe2x80x9d position of the dispensing gun. Upon initial application of the dispensing gun causing retraction of the metering rod, a generally constant orifice exists between the cylindrical tip portion of the metering rod and the cylindrical opening of the valve seat to permit constant xe2x80x9cfinexe2x80x9d metering of the components until the cylindrical tip portion of the metering rod is fully within the frusto-conical portion of the valve seat whereat variable metering occurs as described above.
In accordance with another aspect of the invention, the detachable nozzle connected in a sealing manner to the nose surface of the gun has an outlet tip at one end, an inlet chamber at its opposite end adjacent the nose and a static mixing chamber containing the static mixer therebetween. The cross-sectional area of the inlet chamber at a position adjacent the nose surface of the dispensing gun is larger than the cross-sectional area of the inlet chamber at its intersection with the mixing chamber and the inlet chamber is generally formed as a truncated cone which funnels each component along the walls thereof into the mixing chamber in a manner which alleviates turbulent flow and tends to maintain the components unmixed until reaching the static mixer. An advantage of this nozzle design is the increase in xe2x80x9cclogging timexe2x80x9d, a desirable feature, which is the time it takes curing foam to clog an attached nozzle after a gun has been recently used. Thus, the non-turbulent flow reducing characteristics of the gun characterized by the geometry of the dispensing passages, feed passages and metering rods described above is continued in the nozzle design, all of which contribute to the ability of the gun to maintain ratio control of the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d liquid components, maximize flow output and extend the xe2x80x9ccloggingxe2x80x9d time.
In accordance with another aspect of the invention, an improvement is provided in a detachable nozzle for use in a two-component dispensing gun having a pair of valve seat openings formed in two protrusions which extend from the nose of the gun through which each component is dispensed. The improved nozzle has a back plate filling and closing one end of the nozzle and the back plate has a pair of cup shaped recesses for receiving the protrusions when the nozzle is attached to the dispensing gun with the back plate adjacent or abutting the nose of the dispensing gun. Each cup shaped recess has a valve extension seat opening which is in registry with the valve seat opening in each protrusion. A resilient strip of material pinned to the back plate and extending over a valve seat extension opening is provided. The resilient material flexes out of contact with the valve seat extension opening when the pressure of the liquid component discharge through the valve seat opening is greater than the pressure of the liquid components in the nozzle. Importantly, when the pressure of the liquid components within the nozzle is greater than the pressure of the liquid components in the protrusion, the resilient strip seals the valve seat extension opening whereby cross-over into the dispensing gun between the liquids within the nozzle is alleviated.
In accordance with a still further feature of the invention, the stiffness of the resilient material in the nozzle is chosen depending on the dispensing gun application. Generally, the resilient material may have sufficient rigidity to seal valve extension opening when the pressure of the liquid component in the gun is below a set pressure whereby post drip of the dispensing gun is improved when metering is stopped. Alternatively, the dispensing gun may be supplied with xe2x80x9cfinexe2x80x9d metering nozzles which may be equipped with relatively stiff resilient material to cause fine metering of the components.
In accordance with still another important aspect of the invention, the back plate and the nozzle in the valve seat protrusions extending from the gun""s nose are plastic and the exterior surface of the base of the cup shaped recess has a sealing ring concentric with the valve seat extension opening formed in the recess. By selecting plastics of different hardness, the sealing ring resiliently deforms or is resiliently deformed by the end face of the protrusion when the nozzle is affixed to the dispensing gun.
In accordance with still yet another aspect of the invention, the metering rod""s generally cylindrical tip portion extends into the valve seat""s extension opening in the cup shaped recess of the back. The valve seat""s extension opening may have a smaller or equal diameter to the valve seat""s minor frusto-conical diameter in the gun protrusions providing a generally constant fine metering of the components at initial actuation of the trigger whereat the cammed surface on the annular collar of the metering rod provides increased travel of the trigger lever.
In accordance with a still further aspect of the invention, the dispensing gun has a handle body portion transversely extending from a spring body portion of the dispensing gun and adjacent the trigger lever. The handle has at least one groove formed therein opening to face the trigger lever and the trigger lever has a transversely extending trigger lever recess which opens to the handle portion. A lock tab is provided which is pivotably mounted within the trigger lever recess and is operator actuated from a stored position where the lock tab is contained within the trigger lever recess to a locked position whereat the lock tab is pivoted out of the trigger lever recess into the groove rendering the dispensing gun inoperable for dispensing the foam components. Significantly, the handle has a plurality of grooves which open to the trigger lever and are transversely spaced at set distances on the handle and the lock tab is pivotably movable out of the trigger recess to positions aligned with any one of the handle grooves whereby slow or fine metering of the gun can be positively controlled by the locking tab.
It is thus an object of the invention to provide a two-component dispensing gun which is able to maintain ratio control of the components over a wide flow range.
It is another object of the present invention to provide a two-component dispensing gun which is able to achieve fine or slow metering of the components, either through variable metering or, alternatively, constant metering over a fine metering range.
Yet another object of the invention is to provide a two-component dispensing gun which is able to accurately meter the components in a controllable manner over the complete flow/pressure ranges of the dispensing gun, i.e., from a wide open, full flow condition to slow, low flow, condition.
A still further object of the invention is to provide a two-component dispensing gun which, through its design, allows maximum achievable flow rates in a progressively variable metering manner to be realized for a wide combination of chemical formulations/pressures used in the xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d froth of two-component polyurethane foams.
It is another object of the invention to provide a two-component dispensing gun which alleviates cross-over.
Still a further object of the invention is to provide an improved nozzle for use in a two-component dispensing gun.
Still another object of the invention is to provide a two-component dispensing gun suitable for a wide range of in situ applications of polyurethane foam having different formulations with the only change required to the dispensing gun for the significantly different applications being the supply of different, detachable, throw-away nozzles for significantly different dispensing gun applications.
Still another general object of the present invention is to provide a two-component dispensing gun which is inexpensive to manufacture, simple in design and has a wide range of applications.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth below taken in conjunction with the drawings.